The present invention relates to an optical scanner, more particularly to a multi-beam optical scanner.
In a multi-beam optical scanner, the same plane is scanned with a plurality of light beams that are incident on it simultaneously. In order to prevent undesired phenomena such as a variation in distance between adjacent beams on the plane being scanned, it has been proposed in Unexamined Published Japanese Patent Application (kokai) Nos. 274151/1997 and 209596/1995 that optics be provided in such a way that a plurality of light beams are incident on the plane to be scanned parallel to each other in a secondary scanning direction.
A problem with the multi-beam optical scanner is that if the position of the plane to be scanned is shifted along the optical axis, the distance between adjacent light beams varies not only in a secondary scanning direction but also in a primary scanning direction. In particular, in a case where a plurality of light beams are arranged at an angle with respect to scanning lines either one-dimensionally (as shown in FIG. 4a) or two-dimensionally (as shown in FIG. 4b), the variation in distance between adjacent light beams in the primary scanning direction will cause a straight line crossing the scanning lines to be imaged as a jaggy line, and thus a smooth straight line cannot be represented.
The present invention has been accomplished under these circumstances and has as an object providing a multi-beam optical scanner which is free from the problem of variations in the distance between adjacent light beams in a primary scanning direction notwithstanding a shift of the plane to be scanned along the optical axis.
This object of the present invention can be attained by an optical scanner that deflects a plurality of adjacent light beams across a plane to be scanned in a primary scanning direction and which causes relative movement of the plane to be scanned in a secondary scanning direction perpendicular to the primary scanning direction, wherein said plurality of light beams are allowed to be incident substantially parallel to each other on the plane to be scanned in the primary scanning direction.
The object can also be attained by another optical scanner comprising shaping optics by which a plurality of light beams issued from mutually adjacent light emitting portions are shaped to be substantially parallel at least in a primary scanning direction, a deflector having reflecting faces that reflect and deflect said plurality of light beams and scanning optics by which the plurality of light beams reflected and deflected by the reflecting faces of said deflector are scanned across the plane to be scanned as a plurality of adjacent beam spots, wherein said plurality of light beams cross one another near the front focus of said scanning optics in the primary scanning direction.
The same object can be attained by another optical scanner comprising shaping optics by which a plurality of light beams issued from mutually adjacent light emitting portions are shaped to be substantially parallel at least in a primary scanning direction, a deflector having reflecting faces that reflect and deflect said plurality of light beams and scanning optics by which the plurality of light beams reflected and deflected by the reflecting faces of said deflector are scanned across the plane to be scanned as a plurality of adjacent beam spots, wherein the distance from the rear principal plane of said shaping optics to the front principal plane of said scanning optics is expressed by f1+f2, where f1 is the focal length of said shaping optics in the primary scanning direction and f2 is the focal length of said scanning optics.
The same object can be attained by yet another optical scanner comprising shaping optics by which a plurality of light beams issued from mutually adjacent light emitting portions are shaped to be substantially parallel at least in a primary scanning direction, a deflector having reflecting faces that reflect and deflect said plurality of light beams and scanning optics by which the plurality of light beams reflected and deflected by the reflecting faces of said deflector are scanned across the plane to be scanned as a plurality of adjacent beam spots, wherein said shaping optics and said scanning optics compose afocal optics in the primary scanning direction.
Any one of these optical scanners is desirably adapted to be such that the plurality of light beams are allowed to be incident substantially parallel to each other on the plane to be scanned in the secondary scanning direction.
In the optical scanners of the invention, a plurality of light beams are allowed to be incident substantially parallel to each other on the plane to be scanned in the primary scanning direction. Therefore, the distance between adjacent light beams does not change in the primary scanning direction even if the plane to be scanned shifts along the optical axis. A plurality of light beams may be arranged either one-dimensionally or two-dimensionally at an angle with respect to scanning lines and yet lines crossing the scanning lines can be drawn as smooth lines in an accurate and consistent manner.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 11-176404 (filed on Jun. 23, 1999), which is expressly incorporated herein by reference in its entirety.